The ultimate objective of this work is to understand how receptors and other DNA-binding proteins interact to regulate the transcription of tissue- and hormone-specific genes. The aim of this proposal is to understand how PRL augments the progesterone-dependent transcription of the UG gene by regulating as many as four proteins that bind to the UG promoter. This goal will be achieved by 1) cloning and characterizing the cDNAs for PRL/progesterone-dependent proteins that bind to the UG promoter; 2) determining whether PRL, in combination with progesterone, regulates the sequence-specific binding activity of the UG promoter binding (UGPB) proteins; 3) quantifying hormone-dependent changes in the expression of mRNA for UGPB proteins by specific uterine cell types; 4) characterizing the interactions of PRL and progesterone in the regulation of the UG promoter in an in vitro cell transfection system.